Working ship

ABSTRACT

A working ship ( 1 ), comprising a hull ( 2 ) provided with driving means and a deck ( 3 ). The hull ( 2 ) is temporarily submersible. The deck ( 3 ) is connected to the hull by using connecting means ( 8 ) at an adjustable intermediate distance. The working ship ( 1 ) is thus adjustable between a floating position in which the deck ( 3 ) is located near the hull and a semi-submerged position in which the hull is located substantially below the water surface and the deck ( 3 ) is located above the water surface at a distance from the hull.

RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national phase application ofPCT/NL99/00798 (WO 00/38977) filed on Dec. 23, 1999, entitled “WorkingShip,” which claims priority to the Netherlands Application Number1010884, filed Dec. 23, 1998.

The invention relates to a working ship for carrying out offshoreoperations, in particular for preparing and/or exploiting extractingsites of natural resources, such as oil and gas.

During the offshore extraction of natural resources, there is anincreasing need for exploitation of extracting sites that are locatedrelatively far away front the shore and/or at a relatively great depth.According to present insights, it is believed that about 65% of the oilsupply to be extracted offshore is located in regions relatively faraway from the shore where the sea floor is located at a depth of atleast 2000 m.

When preparing and exploiting such extracting sites, preparation andexploitation operations have to be carried out on the extracting site.When preparing and exploiting an oil extracting site, these operationsconsist in, among other things, the steps of placing of a valve on thesea floor, providing a riser pipe construction between the valve and thesea surface, drilling the oil supply in the soil and making it ready forproduction, extracting oil from the soil, optionally storing and/orprocessing oil, and discharging the extracted oil.

Because of the relatively great distance from the shore and/or therelatively great depth of the sea floor, it has been found to be aproblem to prepare and exploit such extracting sites economically. Whenthe extracting site is located at a relatively great distance from theshore, for instance stores and personnel can be transported by air onlyto a very limited extent. Consequently, stores and personnel have to betransported relatively fast over the sea to the working site, and on theworking site sufficient storage capacity has to be available. When theworking site is located at a relatively great depth, it is not possibleto provide on the working site a working platform supported by the seafloor.

It has already been proposed that operations for preparing andexploiting such extracting sites be carried out by using a so-called“semi-submersible”. Such a construction comprises a rectangular deckplaced on legs. The legs are connected by using floats located below thewater surface. Such a semi-submersible is adjustable by varying thefloating power of the floats between a floating position in which thedeck is located at a relatively great distance from the water surfaceand a semi-submerged position in which the deck is located relativelyclose to the water surface. In the floating position, thesemi-submersible is transported to the extracting site to subsequentlyfunction, in the semi-submerged position, as working platform. It is adisadvantage of such a semi-submersible that it cannot sailindependently to a faraway working site but has to be towed to theextracting site by a tugboat. Furthermore, the sailing speed of such aconstruction is limited so that transport to such a faraway extractingsite takes too long. Moreover, the center of gravity of such aconstruction is located relatively high so that even if few stores arecarried along on the deck there is a risk of capsizing. The risk ofcapsizing is even increased during the adjustment from the floatingposition to the semi-submerged position.

U.S. Pat. No. 3,837,309 describes a semi-submersible construction havingthe features of the preamble of claim 1. The construction is capable ofbeing moved under its own power and has a block-shaped, rectangularhull.

FR 1 366 164 describes a semi-submersible having a block-shaped storagetank that, during transport, is used as a hull.

It has also been proposed that the preparation and exploitation of suchextracting sites which are far away and/or located at a great depth becarried out by using a working ship with a conventional hull providedwith driving means. Such a ship having an elongate hull is described inGB 2 150 516. It is a disadvantage of such a ship that when lying stillon the extracting site it follows wave motions of the water surface toomuch. Consequently, the deck is often not stable enough to carry out thepreparing or exploiting operations. This leads to a greatly decreasedproductivity.

It is an object of the invention to provide a ship that does not havethe above disadvantages. To this end, a working ship according to theinvention comprises a hull provided with driving means and a deck, whichhull is temporarily submersible, and which deck is adjustably connectedat an adjustable intermediate distance to the hull by connecting meansso that the working ship is adjustable between a floating position inwhich the deck is located near the hull and a semi-submerged position inwhich the hull is located substantially below the water surface and thedeck is located above the water surface at a distance from the hull.

Preferably, the hull is of elongate shape, having a length to widthratio of more than 3:1. More preferably the hull has a length to widthratio ranging from approximately 4:1 to 5:1. Such a hull of elongateshape provides for a high sailing speed at relatively low engine powerand fuel consumption. Surprisingly it has been found that, both in thefloating position and in the working position, the elongate hullprovides for ample stability. Due to its elongate shape, thelongitudinal hull can be positioned with its longitudinal axissubstantially transverse to the waves and/or substantially parallel tothe wind. This greatly improves operating conditions in the submerged orfloating position compared to a waking vessel with a substantiallysquare hull, having a length to width ratio of approximately 1:1. Also,during transition from the floating position to the submerged position,such positioning can improve stability.

The effect thus achieved is that in the floating position the workingship can sail to the extracting site independently, without a risk ofcapsizing, fast, and provided with sufficient stores, while in thesemi-submerged position it is sufficiently stable on the extractingsite. In the semi-submerged position, the surface of the working shiplocated near the water surface is relatively small, while a great partof the total weight of the working ship is located below the watersurface. Consequently, the deck, even when much wind and/or high wavesare present, will be sufficiently stable to enable the operations to becarried out. To increase the stability, the hull, in the semi-submergedcondition, can comprise more than 50%, preferably more than 60% of thetotal weight of the working ship. For an optimum stability, the centerof gravity of the working ship in the semi-submerged condition islocated near or below the water surface.

It is observed that when in this context reference is made to a hull,this is a single hull, that is to say a hull forming one floating body.It is further observed that the working ship can also be used on sitesother than extracting sites, for instance to lay pipelines on the seafloor. Consequently, reference will hereinafter be made to the workingsite of the working ship.

Further elaborations of advantageous embodiments of the working ship aredescribed in the subclaims.

The invention will be explained in more detail with reference to anexemplary embodiment shown in a drawing. In the drawing:

FIG. 1 is a diagrammatic side view of a working ship according to theinvention in the floating position;

FIG. 2 is a diagrammatic side view of a working whip according to theinvention in the semi-submerged position;

FIG. 3 is a diagrammatic top plan view of the working ship of FIG. 1,taken on the line III—III;

FIG. 4 is a diagrammatic top plan view of the working ship of FIG. 1,taken on the line IV—IV; and

FIG. 5 is a diagrammatic cross-section of the working ship of FIG. 2,taken on the line V—V, while omitting a number of details.

It is observed that the figures are only diagrammatic representations ofa preferred embodiment of a working ship according to the invention. Inthe figures similar or corresponding parts are indicated with the samereference numerals.

FIG. 1 shows a working ship 1 in a floating position. In the floatingposition or “transport position”, the ship can sail over the sea to aworking site. The working ship 1 comprises a hull 2 and a deck 3. Thehull 2 forms a single floating body and is temporarily submersible. Thehull 2 is provided with driving means 4 and has a streamlined hull formwhich at least partly corresponds to the hull form of conventionalseagoing ships so that in connection with the great distance to betravelled the working ship can sail sufficiently fast in the transportposition, for instance at a speed of at least 15 knots.

The deck 3 is connected with the hull 2 by using connecting means 5 atan adjustable intermediate distance. The working ship 1 is adjustablebetween the floating position shown in FIG. 1 in which the deck 3 issituated near the hull 2 and a semi-submerged position shown in FIG. 2.Referring to FIG. 2, the deck 3 is situated at a distance from the hull2 and the hull 2 is situated substantially below the water surface 6.When the working ship 1 has arrived on the working site, the workingship is adjusted from the transport position to the semi-submerged or“working” position. The adjustment is carried out by reducing thefloating power of the hull 2. This can advantageously be done byproviding the hull with ballast tanks 7 and with control means forcontrolling the amount of ballast stored in the ballast tanks.Furthermore, the intermediate distance between the deck 3 and the hull 2is adjusted to a greater value by using connecting means 5 so that thedeck 3 is located above the water surface 6 at a distance from the hull2.

The connecting means 5 are designed as legs 8 which are rigidlyconnected to the hull 2, while the deck 3 is provided with hoisting orlifting means to enable distance adjustment of the deck 2 relative tothe hull 2 along the legs 8. The effect thus achieved is that, on theone hand, the connection between the hull 2 and the legs 8 can be simplyand reliably made watertight, while, on the other hand, the adjustmentof the intermediate distance between the hull 2 and the deck 3 can beeffected by using conventional hoisting or lifting means as used in theoffshore industry, for instance to enable a working deck of a drillingplatform to be moved along the legs. Preferably, four legs 8 are used,the legs 8 being provided with racks, and the deck 3 being provided withpinions near the legs 8. It is of course also possible to use more orfewer legs 8. It is observed that it is of course also possible toconstruct the connecting means differently, for instance as legs 8 whichare rigidly connected to the deck 3 and can be moved along the hull 2.

The working ship 1 can be positioned on the working site by using adynamic positioning device, for instance four or eight independentlydriven screws disposed crosswise relative to each other. In less deepwater, the working ship 1 can of course also be anchored on the workingsite by means of ground anchors. Depending on the operations to becarried out by the working ship 1, the deck 3 may be provided withdifferent types of installations. Thus, for instance, the deck may beprovided with a pipelaying device 9 for laying a pipeline 11 built upfrom pipe segments 10 over the sea floor. In such a cage, the workingship 1 will in the working position move slowly during the laying of thepipeline 10. A store of pipe segments 10 may then be kept in the hull 2in a manner described hereinafter.

Furthermore, the working ship 1 can be used as crane ship. In such acase, a crane 12 or a lifting device of another type may be provided ona deck 3 to carry out hoisting or lifting operations. It is observedthat such a lifting device may also be used to lift the deck 3 relativeto the legs 8 or to carry out the deck 3 or to carry out pile drivingoperations at sea.

The working ship 1 will hereinafter be described in more detail in a useas offshore working ship for preparing and exploiting an oil extractingsite.

From a harbor, the working ship 1 sails independently in the transportposition shown in FIG. 1 to an oil extracting site located at a greatdistance from a harbor, which site has to be prepared for exploitationand then has to be exploited. For the purpose of navigation, the deck 3of the working ship 1 is provided with a bridge 13. The roof of thebridge 13 is advantageously arranged to be a helicopter landing site 14.Referring to FIG. 4, the deck 3 comprises a number of levels containingworking spaces and sleeping apartments for persons, such as changingrooms 15, sleeping rooms 16, recreation rooms 17, dry and cooledstorerooms 18, washrooms 19, pumping rooms 20, generator rooms 21,laboratories 22, etc. In the transport position, the amount of ballaststored in the ballast tanks 7 is relatively small so that the hull 2 hasso much floating power that it is located at least partly above thewater surface 6.

The hull 2 comprises storage rooms for keeping stores, such as water,fuel, spare parts, and other production aids (FIG. 3). By making thelegs 8 hollow, it is achieved that the interior of the hull 2 isaccessible, for instance for loading the interior of the hull 2. In FIG.3 it is also visible that the legs 8 comprise a double-walled collisionzone 8A.

Advantageously, the hull 2 comprises at least one storage space 23 forvertically storing pipe segments, such as riser pipe segments 24 and/ordrilling pipe segments 25. By storing such pipe segments in the hull,the center of gravity of the working ship can be lowered so as tominimize the risk of capsizing. Consequently, the working ship 1, inparticular in the transport position, is much more stable than asemi-submersible. By storing riser pipe or drilling pipe segments 24, 25in the vertical position, it is achieved that these segments, apart frombeing efficiently stored, can also be readily introduced into theinterior of the hull 2 and removed therefrom. This will hereinafter beexplained in more detail.

When the width of the working ship 1 is chosen smaller than 31.5 m andthe amount of ballast in the ballast tank 7 in adjusted by the controlmeans so that the hull 2 will be temporarily located relatively farabove the water surface, it can be achieved that, if desired, theworking ship can make use of the Panama Canal to reduce the itinerary tothe working site. This is shown in FIG. 1 by a water line 6A.

Once arrived on the working site, the ballast tanks 7 are filled withballast, for instance water, and the hull 2 is submerged to below thewater surface 6 (FIG. 2). Furthermore, the deck 3 is moved up along thelegs 8 by using lifting means not shown in the figure so that the deck 3is located above the water surface 6 at a distance from the hull 2. Inthis working position, the deck 3 is sufficiently stable for carryingout operations thereon.

To prepare the extracting site for production, a valve block is loweredby using a crane 12 from the deck 3 onto the sea floor. To facilitatethis, the hull 2 comprises a channel 26 extending substantiallyvertically through the hull 2 and an opening 27 in the deck 3,corresponding with the channel 26, so that the water is accessible fromthe deck 3 via the opening 27 and the channel 26. Via the opening 27 andthe channel 26, other objects, such as robots, can of course also belowered into the water. Furthermore, other operations can be carried outvia the opening 27 and the channel 26, for instance pile drivingoperations to fix a valve onto the sea floor. To disturb the streamlineof the hull 2 as less as possible, the channel 27 can be provided with aclosure near the bottom of the hull 2. Of course, it can also beadvantageous to close the channel 26 and/or the opening 27 in otherplaces, for instance for safety purposes.

Referring to FIG. 1, FIG. 2, and FIG. 5, the working ship 1 furthercomprises a substantially vertically disposed working column 28 forprocessing riser pipe or drilling pipe constructions or other offshoreinstallations. In the embodiment shown, there is provided a centralworking column 28 having a channel 26 extending therein. The workingcolumn 28 also extends through the opening 27 in the deck 3 (FIG. 5).The working column 28 comprises a suspension device 30 for suspending ariser pipe or drilling pipe construction. In the semi-submergedcondition of the working ship 1, the interior of the hull 2 isaccessible via the hollow legs 8 and the working column 28.

The advantage of providing the working column 28 with an integratedchannel 26 is that a shielded environment is created that provides bothaccess to the hull and the water. In particular, the effect of wind andwaves while hoisting and lowering objects from and into the water can beminimised by providing the shielded environment.

After a valve has been placed on the sea floor, riser pipe segments 24are transported from the hull 2 via the working column 28 to the deck 3.To this end, the working ship 1 comprises vertical transport means 31for moving riser pipe segments 24 vertically up and down via theinterior of the legs 8 or the working column 28. Disposed in the hull 2are moving means 32 for subsequently moving the riser pipe segments 24vertically sidewards (FIG. 2). When building up a riser pipeconstruction, the riser pipe segments 24 are first transported fromtheir storage space 23 to the working column 28 by using the horizontalmoving means 32 and subsequently moved up vertically to the height ofthe deck 3 by using vertical moving means 31. Then the riser pipesegment 24 is placed above the channel 26, for instance by using a crane12 or further horizontal moving means, and attached to the suspensiondevice 30. In the working column with integrated channel, the riserpipes need in essence only be moved up and down and need not bereoriented. Then a next riser pipe segment 24 is supplied in the samemanner and coupled to the preceding riser pipe segment 24. Each timewhen a riser pipe segment 24 has been coupled, the suspension device 30is coupled off and the riser pipe 34 formed by the coupled riser pipesegments 24 is lowered by using hoisting means 35 and gripped again byusing the suspension device 30. As soon as the riser pipe 34 has reachedthe sea floor, it is coupled to the valve. During the operations,possible movements of the working ship 1 relative to the riser pipe 34are compensated by using the spacer means axially movable within thechannel 26, such as hydraulic telescopic cylinders 36.

To enable the drilling of the oil well, drilling pipe segments 25 can besupplied in the same manner as the riser pipe segments 24. The furtherpreparation of the extracting site for production in not explained inmore detail, since it will be clear to those skilled in the art. It isobserved, however, that by carrying out the process described in reverseorder the riser pipe and drilling pipe segments 24, 25 can be broughtback into the hull 2.

As soon as the oil well is ready for production, oil is supplied via theriser pipe 34 and, optionally after a first process step, discharged viaa pipeline 11 to the shore or to a storage ship. The hull 2 may alsocomprise one or more storage tanks for storing oil extracted by usingthe working ship (FIG. 3). If the storage tanks are made sufficientlylarge, the working ship can also function as so-called FPSO or storageship. During the filling of the storage tank, the amount of ballaststored in the ballast tanks 7, of course, has to be controlled by usingthe control means so as to maintain the correct floating power of thehull 2. It is observed that the working column 28 may also be disposedeccentrically on the ship.

Also provided is an auxiliary working column 29. In such an auxiliaryworking column 29, parts of riser pipe or drilling pipe constructionscan be built up simultaneously in an analogous manner as describedbefore and then be lowered into the water via the working column 28 orvia a channel 26 disposed in the auxiliary working column 29. Thisenables not only a more rapid building up of a riser pipe or drillingpipe construction but also the normal continuation of the compositionduring heavy weather when the riser pipe construction has to be coupledoff the working ship 1. Of course, such an auxiliary working column canalso be used when dismantling constructions.

Furthermore, the interior of at least one of the legs or working columnsmay advantageously be provided with means for passing a winch rope of aground anchor and with means for storing an anchor cable. It is thusachieved that a great length of winch ropes and anchor cables can bestored efficiently.

It is observed that the constructional parts of the working ship are notdescribed in more detail, since they will be clear to those skilled inthe art.

It is further observed that the invention is not limited to theexemplary embodiment shown herein. Many variations thereof are possiblewithin the scope of the following claims.

What is claimed is:
 1. A working ship for transport on a water surfaceand carrying out of off-shore operations at a working site on a watersurface, the working ship comprising a single hull and a deck, said hullforming a floating body and being provided with driving means, said deckbeing located at all times during transport and at a working site abovethe water surface, said hull being temporarily submersible duringoff-shore operations, and said deck being connected to the hull by usingconnecting means at an adjustable intermediate distance so that theworking ship is adjustable between a floating position in which the deckis located above the water surface and near the hull and asemi-submerged position in which the hull is located substantially belowthe water surface and the deck is located above the water surface at adistance from the hull, wherein the hull is of elongate shape, having alength to width ratio of more than 3:1.
 2. The working ship according toclaim 1, wherein the hull has a length to width ratio ranging fromapproximately 4:1 to 5:1.
 3. The working ship according to claim 1,wherein the connecting means comprise legs which are rigidly connectedto the hull, and wherein the deck is provided with hoisting or liftingmeans to enable distance adjustment of the deck relative to the hullalong the legs.
 4. The working ship according to claim 1, wherein in thesemi-submerged condition the hull comprises more than 50%, of the totalweight of the working ship.
 5. The working ship of claim 4 wherien thesemi-submerged condition of the hull comprises more than 60% of thetotal weight of the working ship.
 6. The working ship according claim 1,wherein in the semi-submerged condition the center of gravity of theworking ship is located near or below the water surface.
 7. The workingship according to claim 1, wherein the hull comprises at least oneballast tank and control means for controlling an amount of ballaststored in the ballast tank.
 8. The working ship according to claim 1,wherein the hull comprises at least one storage tank for storing rawmaterial extracted by using the working ship, said storage tank furthercomprising supply and discharge means for supplying the extracted rawmaterial to the storage tank and discharging it therefrom.
 9. Theworking ship according to claim 1, wherein the hull comprises at leastone storage space for vertically storing riser pipe segments, drillingpipe segments or both.
 10. The working ship according to claim 1,wherein there is provided at least one substantially vertically disposedworking column for processing riser pipe, drilling pipe constructions orother offshore installations.
 11. The working ship according to claim10, wherein the at least one working column comprises a suspensiondevice for suspending a riser pipe or drilling pipe construction. 12.The working ship according to claim 11, wherein the hull comprises achannel extending substantially vertically through the hull and anopening in the deck, corresponding with the channel, so that the wateris accessible from the deck via the opening and the channel, the channelextending within the working column.
 13. The working ship according toclaim 10, wherein an interior of the hull, at least in semi-submergedcondition of the working ship, is accessible via an interior of theconnecting means, the working column or both.
 14. The working shipaccording to claim 13, wherein there are provided vertical transportmeans for moving riser pipe and/or drilling pipe segments vertically upand down via the interior of the connecting means and/or the workingcolumn, and wherein horizontal moving means are provided in the hull formoving the riser pipe and/or, drilling pipe segments horizontally. 15.The working ship according to claim 10, wherein the interior of at leastone of the connecting means and/or working columns is provided withmeans for passing a winch rope, means for storing an anchor cable orboth.
 16. The working ship according to claim 10 further comprising thehull having a channel extending substantially vertically through thehull and an opening in the deck, corresponding with the channel, so thatthe water is accessible from the deck via the opening and the channeland a suspension device for suspending a riser pipe or a drilling pipeconstruction, the suspension device being operatively associated with atleast one of the channel and the at least one working column.
 17. Theworking ship according to claim 1, wherein the hull comprises a channelextending substantially vertically through the hull and an opening inthe deck, corresponding with the channel, so that the water isaccessible from the deck via the opening and the channel.
 18. Theworking ship according to claim 17, wherein the channel is closable atleast near the bottom of the hull.
 19. The working ship according toclaim 1, wherein there is provided a hoisting, pile-driving device orboth.
 20. The working ship according to claim 1, wherein there isprovided a pipelaying device.